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Porting an alloy head

Last post 07-27-2008, 4:00 PM by motorbill66. 10 replies.
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  •  05-06-2008, 5:54 PM 14283

    Porting an alloy head

    I am hoping to get one of you out there in the community to help me with a sourcing decision.

     

    I have ordered the new Moss Supercharger Kit for a 5 bearing MGB engine.

    Now I am down to the sourcing of an alloy head for my B.  Keep in mind I will be using the Moss supplied manifold to make up to the head. I would like to find someone who will do an excellent job of porting the head and could supply the head as well so I only need to write one order for the head delivered complete, ported and assembled with valves, springs, and retainers.

    Now the Moss supplied manifold is a completely different animal. Has anyone seen it yet? Does it come fairly smooth with good transitions or does it have to go out to be polished as well?

    I am using a 270 cam.

  •  05-07-2008, 9:22 AM 14288 in reply to 14283

    Re: Porting an alloy head

    Ditty,

    I'm not the resident supercharger expert, but I do know that's easy to go too far with camshaft specs when you supercharge an otherwise relatively stock engine. Also, since the manifold and head will be pressurized, porting is of somewhat limited value. The intake ports on the non-crossflow alloy head commonly available have been criticized by some as already being too large. Smoothing the exhausts might be good, but frankly, bang for the buck wise, I wouldn't go much further. Kelvin Dodd, where are you?

    Bill


    Motorbill
    From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon
  •  05-08-2008, 2:01 PM 14303 in reply to 14288

    Re: Porting an alloy head

    Well, I'm no Kelvin Dodd, but I did drive the Roach, my blown MG Midget, to Buttonwillow last weekend. Does that count?

    Motorbill I will respectfully disagree as to the value of port work on a supercharged motor. Other than camshaft design, the same principals which work on a normally aspirated motor work on a supercharged motor. The better the head flows, the more power you can make. You can always make more boost, but there is a point at which, due to air flow restrictions in the ports/valves, no more air can be shoved through the head.

    Sean Brown at www.flowspeed.com ported the alloy head on my Midget. After he did the work I lost 1-1.5 pounds of boost. To get back to the origianl boost level required a smaller blower pulley. Within its operating parameters, the blower produces a higher volume of air relative the speed it turns. If I have to spin the blower faster to maintain the same pressure level in the inlet manifold, this means more air is passing through the motor.

    In other words, the cylinder head has been made less of a restriction, and the motor is using more air. More air, more fuel, more mojo baby! Afriend is currently building a TR4 engine on my behalf. I don't know if we will produce a TR3/4 supercharger kit or not, but the cylinder head work being done is the same regardless, and it's all about creating less air flow restriction through the head.

    Sean Brown was not overly enthusiastic about stock porting on the alloy B-series heads. You can see flow bench numbers on his site. I would at least talk to him about your head before completing the motor. He can also match the blower manifold to the head.

    Cheers,

    Robert
     


    Robert Goldman
    VP Business Development
    Moss Motors, Ltd.

    E-mail: rgoldman@mossmotors.com
  •  05-08-2008, 2:14 PM 14304 in reply to 14303

    Re: Porting an alloy head

    Oops, left out cams. A 270 cam will probably be fine. Everyone agrees too much overlap is bad, but in the testing we've done here at Moss that never really came up. In other words, as far as we have ever tried to go with camshafts, they always made more power. Fuel mileage? I don know, but power can be had. The argument is the same as above - more flow more peak power, but at the cost of low end torque.

    The blowers being used on our LBCs can pump way more air than the engines can use, so it's not a question of air supply. If cross talk between the valves is letting some air get past, just spin the blower faster and get your pressure back. On my TR4 motor we're trying a slightly different theory. We're using a more modest cam in conjuntion with high ratio rockers. The theory here being that we get mid range torque without completely sacrificing high end power. The TR was always more of a slow revving stump puller, so the hope is to maximize its strengths.

    RG
     


    Robert Goldman
    VP Business Development
    Moss Motors, Ltd.

    E-mail: rgoldman@mossmotors.com
  •  05-08-2008, 2:51 PM 14305 in reply to 14303

    Re: Porting an alloy head

    Robert,

    I readily defer, but I guess my concern has to do with just how far you want to push a stock, and perhaps somewhat aged, engine. Supercharging always introduces some "unatural" forces. For this reason, most modern superchargers are fairly limited in boost, and dire warnings about ignition timing and total compression accompany them.

    The idea of increasing flow is to process more air per cycle. This increases dynamic compression. Better heads than mine know how much a given engine can take. We recently had to rebuild a TR 4 engine due to an old Judson supercharger and some aggressive timing causing detonation which broke pistons. The use of high performance camshafts, to the best of my understanding, does the same thing by allowing more air through a greater intake valve open time and aperture. Engines are air pumps.

    The more air and fuel you can cram into a combustion chamber, the more air you can pump, obviously. The more air you pump, the greater the strain on the mechanical components. I'm not the one to say how far you can take this process. I tend to err on the conservative side for street engines, bucks being what they are these days. Anyhow, that was my reasoning, but I am certainly not on the absolute leading edge here. Enjoy.


    Motorbill
    From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon
  •  05-08-2008, 4:25 PM 14309 in reply to 14305

    Re: Porting an alloy head

    Bill, 

    Maybe we both should have asked what Mr. Ditty is trying to accomplish. Could be neither of us is really helping him. I understand your desire to preach safety. Far be it from me - a supplier of parts - to be encouraging people to bend stuff (said with tongue in cheek). As you found with your TR customer, timing becomes critical when cylinder pressures rise.

    Regardless of other factors, the higher the boost number the harder it is to get it fueled properly. These modern Eaton blowers will suck a float bowl dry in no time. With high boost levels, this is a recipe for detonation and disaster. I guess I assumed that if someone is willing to spend the money on an alloy head they're looking for more than just stock performance. That being the case, my best advice is to build a good free breathing engine and then give it just enough boost.

    There is a real world correlation between boost number and destruction. Trying to fix a breathing problem by upping the boost will end in tears. If Ditty is looking to run stock supercharged power, then you're absolutely right, he doesn't need to rework the head.

    RG
     


    Robert Goldman
    VP Business Development
    Moss Motors, Ltd.

    E-mail: rgoldman@mossmotors.com
  •  05-10-2008, 6:09 AM 14338 in reply to 14309

    Re: Porting an alloy head

    the objective is to get the most out of the engine I can get without having to be under the hood everyday. The supercharger option looked like the best solution and was preferred to the double DCOE options out there. The battle of vacuum vs boost will always be won by the boost solution. Don't you think

    Granted going to forged pistions and uprating the bottom half is expensive but that part is done. The stock Supercharger pulley with the high compression B motor looked like a good fit across the power range. On the exhaust side I have gone big bore, with the Monza headers. The Mallory distributor (optical). The Alloy head is simply to run the engine cooler and dissipate the heat of the superchargered fuel burn faster. Porting the head just seemed like the logical step. Yes it adds cost, but you have answered the question about improved flow.

  •  05-10-2008, 7:00 AM 14339 in reply to 14338

    Re: Porting an alloy head

    Ditty,

    Wow! I didn't know you'd already gone that far with 'er. It sounds like you're building up quite a powerplant. How about an alloy radiator? When you make power you inevitably make heat along with it. I bet you're already on this.


    Motorbill
    From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon
  •  07-27-2008, 10:09 AM 15384 in reply to 14283

    Re: Porting an alloy head

    Well the ported head came back from Flowspeed in Orgeon. IT looks great.

    I just need to confirm volumes and I will order my pistons.

    Hopefully Moss will have the Supercharger in the "good book" soon so I can get this rig on the road.

    Shawn Brown at Flowspeed was really easy to work with. Very professional and helpful.

  •  07-27-2008, 10:27 AM 15385 in reply to 14339

    Re: Porting an alloy head

    Do you have a sourcxe you can recommend for an alloy radiator?

    Dittybag

  •  07-27-2008, 4:00 PM 15388 in reply to 15385

    Re: Porting an alloy head

    Ditts,

    Try looking at www.rondavisradiators.com    We're putting one of theirs into a Bugeye restoration with a supercharger right now. It's a really nice looking piece of work. They won't list it directly on the website picture list, but down at the bottom of the stock application radiator "department" you'll see that MG is covered. I'm sure they'll have something for you. You'll have to call. All things considered, the prices are, well, reasonable.

    Enjoy


    Motorbill
    From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon